An image processing apparatus which reads an original on a glass plate and sends image data to a host computer or the like is known. As the original, a document type original such as an article of magazine or the like, and a film type original such as a photographic film are used. In use of the former original, light reflected from the original is read, and in use of the latter original, light transmitted through the original is read. Image processings respectively characteristic of these original types are performed.
As the image sensor of the image processing apparatus, a line sensor such as a CCD is used. Especially, as a sensor for reading a color original, a 3-line color sensor with 3 arrays of line sensors, having color filters formed on photoelectric conversion devices, is often employed. In the image reading apparatus, two-dimensional image data is read by moving the above-described line sensor orthogonally to a direction along the array of photoreception devices.
FIG. 8 is a schematic view showing the structure of the CCD line sensor.
Numeral 802 denotes shift gates which are closed during a storage period. A photoreception device portion 801 accumulates electric charge while performing photoelectric conversion during a photoreception period. When the shift gates 802 are opened, the accumulated electric charge is moved to shift registers 803. At this time, electric charge at odd-numbered photoreception devices and electric charge at even-numbered photoreception devices, in one line, are respectively moved to separate registers on both sides. The moved electric charge are transferred via the shift registers.
FIG. 9 is a timing chart showing a drive pulse and 1-line data processing.
Symbol Hsync denotes a period required for moving the sensor in a subscanning direction to read one line of image, i.e., a period for image processing for one line in the system. Symbol SH denotes a signal supplied to the shift gates of the sensor. When the signal is at a LOW level, the shift gates are closed, on the other hand, when the signal is at a HIGH level, the shift gates are open and accumulated electric charge is transferred to the shift registers. The period of the signal corresponds to the storage period of the line. Numerals φ1 and φ2 denote drive signals for the shift registers. The transfer frequency of the pulses corresponds to the transfer speed. In this manner, all the pixels are transferred as image data within the storage period.
Generally, the image processing apparatus performs various image processings to obtain an ideal output image. Color balance adjustment performed upon color image reading is one of those processings. Generally, in the image sensor, the color balance is not completely adjusted among R, G and B of output signal due to influence of light source lamp and/or color filters.
Further, when a transmission-type original such as a positive film or a negative film is read by the same system, the color balance must be adjusted in consideration of film density or the like as well as the above factors. Especially, when a negative film is read, tonality must be adjusted for each original.
As to these requirements, gain control of analog signal, processing on AD-converted digital data and the like can be made. Further, a color sensor may be supplied with a shutter function to control exposure for each color. In this sensor, photoreception and storage portions are connected to shutter drains. Pulses are supplied to shutter gates to arbitrarily control actual storage periods.
FIG. 10 is a timing chart showing a driving method for the color sensor with the shutter function.
Storage periods SH_R, SH_G and SH_B of 3 color photoreception portions are the same, however, drive signals supplied to shutter gates are different for respective colors. When these signals are at a HIGH level, the gates are opened and electric charge is discharged to the shutter drains, while when the signals are at a LOW level, storage is started. In this manner, the actual electric-charge storage period can be changed for respective colors while synchronizing the 3 color lines. However, this function added to the sensor increases the costs, and further, widens the distance between the lines.